The goal of this research is the biochemical and genetic analysis of cellular growth and development utilizing several eukaryotic model systems. Cellular gene expression and host cell control of the synthesis or metabolism of specific gene products are to be analyzed by studies of endogenous C-type RNA viruses in selected strains of mice. Viral mutants defective in specific viral gene products will be isolated and characterized. Morphological transitions coincident with early development will be examined through the isolation of developmental mutants of the colonial algae, Volvox, so as to structure the genetic control of the pattern of early gonidial cleavages which lead to commitment of either sexual or asexual differentiation. Reactions or processes of cell growth and development regulated by cyclic GMP in vivo, and the mechanism of cyclic GMP function will be elucidated by isolation and characterization of mutants of B. emersonii defective in cyclic GMP synthesis. The mechanism of positional control of cell differentiation will be examined by isolation of colonial populations of interstitial cells of Hydra, and analysis of their potential to differentiate into nerve cells or nematocytes.